Blogs of M. Mizanur Rahman

Currently Scrum is the most popular Agile framework and many teams are willingly or forcefully adopting it. Since Scrum does not work like a magic tonic and cure all problems, sometimes it can create problems by making everything transparent. Another challenge for adopting scrum is the readiness of the team members or management.

In Bangladesh or any other country in the subcontinent, adopting scrum is a big challenge as we struggle with self managed team concept. we love to follow people rather than taking the lead. we are not aware of our potentials and capabilities. As a result we lack in self esteem and motivations.

If you are planning to adopt scrum at your organization, the following suggestions might be very helpful.

Today I spent a lot time to find a suitable library to convert UTF-8 text (specially Bangla) to hexadecimal values. After spending few hours with other online libraries, I have decided to write my own 🙂 these are pretty handy functions if you are using MPDF to create PDF with UTF-8 strings , specially in Bangla.

I was planning to move my blog to under my personal domain and it is now available at www.mizanurrahman.com. It will be an exact copy of this site including all posts and contents. I will be maintaining both of the site together to make sure that the visitors have the current information available in the both site.

Please feel free to ask me any questions. Thanks everyone for the support.

Yes our dream project, “Bangla PHP book” has started last week. Me, Hasin, Emran, Shureed and all those enthusiast developer from PHPXperts group really making it happen. Thanks to Hasin for his initiative and we are very optimistic to bring out a quality book very soon. If anyone is interested, you can join our project. more information on this project can be found here.

Many times I asked this particular question in the interview session and many people failed to answer. This is just to see the analytic ability of a candidate and how dynamic thinking they have. The logic is same for all programming language, so if you have the logic right then you can answer it for any particular language such as PHP, JAVA, C++, C etc. but in this tutorial We will use PHP 🙂

What if we can use the third variable:

$a = 100;

$b = 200;

now we need to swap the values so that $a becomes 2oo and $b becomes 1oo.

the basic technique is to introduce a third variable $tmp

$tmp = $a;

$a = $b;

$b = $tmp;

isn’t it straight forward. introducing a third variable it is so easy. but what will be our approach if there is no third variable? is it possible?

The answer is a big YES. There are several ways and they fall in two types of solution.

1. Arithmetic operation

2. Bitwise operation.

Arithmetic Operation:

we can use addition-deduction and multiply-division method to solve the problem.

let’s see how addition – deduction method works.

<?php

$x = 10;

$y = 20;
$x = $x+$y;
$y = $x – $y;
$x = $x – $y;
?>

it is also very simple, isn’t it. first we are adding the two numbers and keeping the result in one of the variable. in the above example its $x and it contains $x+$y. in the second operation, we are deducting $y from $x and assigning it to $y. now lets break the equation logically

$y = $x – $y => $x + $y – $y => $x // [ since $x = $x+$y ]

cool, we swapped one of the variable. and following the same operation we are swapping the second one in the third line. so that’s it. It is so easy but just requires some logical thinking. do not try to memorize it rather than understand the simple logic here.

now the multiply-division method:

<?php

$x = 10;

$y = 20;
$x = $x*$y;
$y = $x / $y;
$x = $x / $y;
?>

it is same as the addition-deduction method and logic is similar.

now do we see any problem in the above logic? that is the question i ask if someone can answer the question correctly and show me the above solution. 🙂

the answer for that is very simple, it is the number overflow as we always have upper limit for integers. so when we add or multiply two big numbers then the result can cause overflow and might not show desired results.

so what can be a good solution with keeping the overflow fact in mind? the answer is bitwise operation

Bitwise operation:

in order to swap two values we can use the XOR bitwise operator.

Note: A bitwise exclusive or takes two bit patterns of equal length and performs the logical XOR operation on each pair of corresponding bits. The result in each position is 1 if the two bits are different, and 0 if they are the same

the algorithm is

x = x XOR y

y = x XOR y

x = x XOR y

if we write them in computer language using caret (^) then it will look like

x = x ^ y

y = x ^ y

x = x ^ y

in shorter version:

x ^= y

y ^= x

x ^= y

in one line

x ^= y ^= x ^= y

so here is the command in php:

$x ^= $y ^= $x ^= $y

now how it works:

so now we know how to swap two values without using a third variable. ask me any questions you have 🙂

Did you try to run php from command line and faced with php exception like safe mood is on, memory limit exceeded, maximum execution time exceeded etc. A general solution is to edit the php.ini and made those changes and restart apache server. At least i found these solutions online 🙂

But that is not gonna solve your problem. when you are running CLI or shell_exec in *nix environment, php uses a different php.ini file located inside CLI folder. until you edit that the problem wont be solved. So if you are constantly getting errors after altering your php.ini file used by your web server then you should try your CLIs’ php.ini file for any issues regarding cron/CLI.

I was working with MediaWiki Gallery extension named “Smooth Gallery” which is based on JonDesign’s SmoothGallery . It was almost the thing i was looking for but not the exact one for my purpose. As a result I had to hack the code and modify it to fit my needs. You can download the extension and install it for your purpose. I have named it as WikiGallery as lots of things has been changed in this extension. This extension supports external images as well and hence give you more options to create a nice gallery.

Now the extension is ready and we can use it to our wiki pages. Edit a wiki page and add the following tag with image names delimited by the wikigallery delimiter as mentioned on LocalSettings.php file (in this case its n , but it can be , # etc). For local files (uploaded in the wiki), we do not have to put anything. but for external images the http:// must be there.

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About Me

I am Mizanur Rahman from Bangladesh. I am a Software Engineer by profession. I love to work on open source projects and specially web based systems. I am a moderator of the PHPExperts, the largest PHP Users group in Bangladesh.

I have my own startups Informatix Technologies and TechMasters. I am an Agile enthusiast and Scrum practitioner.